PRESERVED BY THE DRY desert air and their isolation, the caves honeycombing a cliff on the fringes of the Han Chinese empire have preserved one of the world's greatest repositories of art for 1,500 years.
Finally, it is the package tourist who is threatening to destroy murals which escaped the ravages of so many rebellions and revolutions 'I've noticed a big change in the past eight to 10 years. You can't see inscriptions so well, there is flaking and foxing - small black and brown dots,' said Professor Sarah Fraser of Northwestern University in Chicago, an expert on Dunhuang art.
In the Tang dynasty it would take Buddhist monks years to travel via Dunhuang to India and bring back sutras, journeys that are the stuff of legends. A century ago, Western explorers like Sir Auriel Stein still needed months to reach this small oasis on the Silk route between the Gobi and Taklamakhan deserts. In the 1940s, Chinese artists fleeing the Japanese invasion spent weeks travelling across the country.
When the current director of the Dunhuang Research Institute, Fan Jinshi, arrived in Dunhuang in 1964, straight from Beijing University, it took her eight days by jeep to reach the caves from Lanzhou, the capital of Gansu province. There was still no road. Even eight years ago, when Professor Fraser started visiting the Mogao grottos, it still took 2.5 days by train from Lanzhou.
Now you can fly directly to Dunhuang from Beijing or Hong Kong in just four or five hours and spend another half hour in a tourist bus.
The guardians of the caves still worry about natural disasters like earthquakes or floods. In June the Daquan River flooded, sweeping away the bridge which tourist buses cross from the airport. Six years earlier fierce sandstorms caused a similar crisis. But it is people who pose the greatest threat.